1. Field of the Invention
The present invention relates to an auto-switching converter with PWM and PFM selection, and more specifically to a converter used to auto-switch either a PWM (pulse width modulation) or a PFM (pulse frequency modulation) module to perform DC to DC or AC to DC in response to variation of the load.
2. Description of the Related Art
Electronic products are used universally, and power supply for electronic products is very important. At present, power for electronic products is universally supplied with a switching technique, and PWM and PFM are two kinds of switching schemes.
The PWM switching technique is used to control the switching action of power switches to supply power to an electronic product when the electronic product is working under a full or heavy load, and at this time, the electronic product produces a transmitting loss and a switching loss. Moreover, when the electronic product is working under a low load with the PWM switching scheme, the transmitting loss is reduced but the switching loss is not, because the frequency of the switching is constant. Therefore, the efficiency of the electronic product is reduced when working under a low load with the PWM switching scheme.
As mentioned above, when the electronic product is working under a low load, the PFM switching technique is usually used to control the switching action of power switches. The frequency of the switching is reduced in response to the load of the electronic product, and the switching loss is reduced for a low load. When the electronic product works under a low load, the efficiency of the electronic product with the PFM switching scheme is higher than that with PWM switching technique.